The present invention relates to an X-ray image pick-up device such as an X-ray television system.
Television camera exposure is determined by an X-ray pick-up tube voltage, its current and an optical diaphragm or stop for variably controlling an amount of light incident on the television camera. Conventionally, exposure is controlled by an X-ray physician who adjusts the tube voltage and tube current so as to keep a maximum value of an output pick-up signal level from the television camera below the certain saturation level in accordance with practical experience and such that the optical diaphragm is adjusted in accordance with the amount of light incident on the television camera. There are various combinations of values of these three factors for setting an output pick-up signal level of the television camera to be a predetermined level. However, there is only one combination of the three factors that achieves the optimal (maximum) density resolution (corresponding to the difference in density between the region of interest in the picture and the region of noninterest). For this reason, it is difficult to determine if the preset combination provides the optimal density resolution. In addition, although a sensor is arranged behind the optical diaphragm (i.e., between the diaphragm and the camera) in the optical system to measure the amount of light incident on the television camera through the optical diaphragm, the sensor measures only the amount of light passing through the central portion of the optical diaphragm. Halation occurs in the peripheral portion of the resultant image. In addition to this disadvantage, a sensor shadow or ghost tends to appear in the image.